for a general dissipative coefficient \(\Upsilon (T,\phi )\) . For constant dissipation with neither \(T\)  or \(\phi \)  dependence, the analytical solution was obtained in [1]}, and the amplitude of the comoving curvature perturbation is given by:
\(P_{{\cal R}_*}^{\rm nogr} = \left( \frac{H_*^2}{2 \pi \dot{\phi }_*} \right)^2 \left( 1 + 2 n_* + \frac{T_*}{H_*}\cdot \frac{2 \sqrt{3} \pi Q_*}{\sqrt{3 + 4 \pi Q_*}}\right) \,. \) 
